utility $H

Creates a Hash (which is synonymous to "map" or "associative array"
for our purposes). A convenience wrapper around the Hash constructor, with a safeguard
that lets you pass an existing Hash object and get it back untouched (instead of
uselessly cloning it).

The $H function is the shorter way to obtain a hash (prior to 1.5 final, it was
the only proper way of getting one).